Luis Signorelli1, 5, Luis E. Hernández-Gutiérrez¹˒², Pablo Pacheco Delgado³, Helena Hernández-Martín¹˒³, Germán D. Padilla¹˒⁴, Gladys V. Rodríguez¹˒⁴ and Nemesio M. Pérez¹˒⁴
¹ Instituto Volcanológico de Canarias (INVOLCAN), 38400 Puerto de la Cruz, Tenerife, Canary Islands, Spain
² Viceconsejería de Infraestructuras, Gobierno de Canarias, 38071 Santa Cruz de Tenerife, Canary Islands, Spain
³ CanaryCarbon, S.L., Avda. de Roma 49, El Sauzal, 38360 Santa Cruz de Tenerife, Spain
⁴ Instituto Tecnológico y de Energías Renovables (ITER), 38600 Granadilla de Abona, Tenerife, Canary Islands, Spain 5 University of La Laguna, Department of Chemistry, C/ Padre Herrera, s/n, 38200 La Laguna, Tenerife, Spain
Abstract: Direct air capture (DAC) with solid adsorbents is limited by the low CO₂ concentration in air and competition from water. This study evaluates commercial zeolite 13X by linking humid-air breakthrough, molecular speciation, thermal regeneration, and reduced-order modelling. Characterization confirmed a predominantly microporous FAU structure with a BET surface area of 710.1 m²·g⁻¹ and a micropore volume of 0.253 cm³·g⁻¹.
Humid ambient-air tests were performed in a fixed-bed reactor with continuous CO₂, H₂O, and O₂ monitoring. Zeolite 13X initially retained CO₂, but subsequently exhibited a pronounced roll-up to C/C₀ ≈ 1.47, showing displacement by the advancing waterfront. Maximum transient CO₂ uptake was 0.0909 mmol·g⁻¹, whereas H₂O loading reached 13.38 mmol·g⁻¹. Staged ex situ FTIR showed that molecularly adsorbed CO₂ decreased as H₂O bands intensified, while carbonate-/bicarbonate-like contributions increased.
Under dry pure CO₂, breakthrough was monotonic and the retained loading reached 3.19 mmol·g⁻¹, confirming that humid-air performance was limited primarily by water competition rather than weak intrinsic CO₂ affinity. Thermal regeneration produced a dominant CO₂ release near 103–107 °C and a broader high-temperature contribution from persistent carbon-containing species and co-adsorbates. Severe regeneration also caused pellet agglomeration and lasting FTIR framework changes. Two hybrid phenomenological models reproduced the H₂O front and CO₂ overshoot using an explicit water-driven displacement term.
Overall, unmodified zeolite 13X is effective for dry CO₂ adsorption but unsuitable for humid DAC without humidity management. Application will require dehumidification, layered beds, hydrophobic modification, optimized cycle termination, or milder regeneration.
Keywords: Direct air capture; Zeolite 13X; Carbon dioxide adsorption; Water competition; Breakthrough curves; FTIR spectroscopy.
Author Profile (first or corresponding author):
Nemesio M. Pérez, INVOLCAN’s Scientist-in-charge, mainly engaged in geochemical research applied to volcano monitoring, surface geothermal exploration, groundwater studies and environmental issues, etc.
E-mail: nperez@iter.es
